1. Field of the Invention
The present invention generally relates to improving performance for devices such as FinFETs. More specifically, the present invention provides a method (and resultant structure) in which localized stressor areas allow carrier mobility in specific regions, such as the FinFET channel, to be separately adjusted for each device.
2. Description of the Related Art
Double gate devices are considered a most suitable choice for next generation devices, since the improved short channel effect control and increased drive current that double gates deliver are needed. One of the most simple double gate devices to fabricate is the FinFET (Field Effect Transistor), due to the front gate and the back gate being self-aligned and the front gate oxide and back gate oxide being processed simultaneously.
FIG. 1 illustrates an exemplary FinFET structure 100 having a single Fin 101, source 102A, drain 102B, and gate 103, as fabricated on buried oxide (BOX) layer 104 on bulk silicon 105. Typically, there are multiple Fin structures in a FinFET joined by Fin connectors, in order to obtain the desired current, similar to increasing gate width W in planar devices.
FIG. 2 illustrates this exemplary FinFET structure 100 in cross-sectional view 200 through the gate 103. The height of the fin is arbitrary, and, as the height is lowered, the FinFET approaches the structure of a planar FET.
FinFETs are known to have improved scaling properties compared to single planar gate devices because the FinFET reduces the short channel effect as channel length is shortened. Strained Si offers improved performance over non-strained channel devices. However, strained Si by SiGe has been challenging to implement, and strained Si by SiGe is even more difficult to implement in FinFETs.
Another advantage of the FinFET is that, since the active areas are all substantially the same size in the length dimension, any stress enhancement in the direction along the current flow is potentially equal in magnitude for all devices. Thus, the mobility improvement and current increase should be substantially similar for all devices.
However, conventional methods to strain Si by SiGe to obtain improvement in nFETs cause more defects, thereby lowering yields. Moreover, it has been very difficult to realize any improvement in pFET performance using the strained Si by the SiGe technique. Therefore, there remains a need to improve performance and reduce costs for FinFETs.